FR2720060A1 - Treating contaminated aq. media e.g. sludges - Google Patents

Abstract

Treatment and purification of liq. media heavily contaminated with suspended and dissolved pollutants involves a succession of gravimetric sepn. phases for removal of solid particles of decreasing grain size and recovery of clarified water. The novelty is that the process includes injecting a precipitant reactant (I) for dissolved components (e.. phosphorus or nitrogen cpds.) leached from cultivated soil by irrigation water. (I) is injected during or after the particle sepn. stages. The obtd. ppte. is then removed, giving a product (specifically water free of phycogenic components) which can be released into natural water-courses.

Description

PROCESS FOR ELIMINATION IN WASTEWATER OR
OF SLUDGE IN PROCESSING, OF CHEMICAL ELEMENTS IN
SOLUTION.

The invention relates to the treatment of wastewater and sludge of various origins.

The invention will more particularly relate to the treatment of polluted and highly charged water, in particular sludge and vases coming especially from operations for the depollution of water bodies, rivers or the like.

Surface natural water reserves, especially rivers, reservoir ponds or lakes, must be subject to clearance operations to eliminate all the foreign constituents that settle there, forming sedimented layers mud or vases.

Physical processes are known that make it possible to take the lower layers of such highly charged water bodies of various origins, in particular organic origins, in order to remove solid particles and suspended solids, which can be evacuated and possibly disposed of in a landfill. while the purified water can be restored to the natural environment from which it comes.

French Patent Application No. 94.01.853, in the name of the Applicant, discloses a method which allows, after being sampled by dragging, under conditions ensuring the perfect immunity of the medium during treatment, vases or sludges sedimented in the bottom of a body of water, these sludge being the subject of successive treatments of screening and grit removal to eliminate most of the solid constituents.

The treatment of the filtrate resulting from these operations may be continued by subsequent dewatering and dewatering phases such as those described in French Patent No. 86.16.201, this subsequent phase providing for the passage over a lamellar separator and a thickener. , followed later by filtration to obtain a purified water largely discharged from its suspended matter (MES), the water can then be released into the original medium by reconstituting the aqueous mass freed of its pollutants.

 It remains however that the chemical compounds in solution present in the liquid medium escape these phases of physical separation.

However, these compounds are particularly harmful to the environment.

This is particularly true in the case, here considered, of the treatment of surface water such as lakes, rivers, reservoirs, etc. in which superficial runoff accumulates.

These waters, because of the leaching of agricultural land, carry with them, in solution, chemical compounds coming from the spreading on the said lands of fertilizers, in particular based on phosphates and nitrates.

These phosphate and nitrogen derivatives accumulate in the natural receiving capacities of natural runoff waters where they continue to produce their desired effect at the outset, in their primary function as chemical fertilizers, elements favoring the phytosynthesis and the development of organisms. plants. '
Within the aqueous medium is developed and, thanks to the presence of phosphate ions, nitrate and to some extent ammonia, a phycogenic action resulting in an algal proliferation.

This accumulation of products promoting plant development also moves with the rivers into the sea and ends, here and near the coast, excessive development of algae.

It is known that the development of aquatic plants, from photosynthesis, necessarily absorbs oxygen which can only be borrowed from the aqueous medium itself.

So that the development of algae in the natural aqueous media, a consequence of the training of agricultural fertilizers, is ruled out by a progressive and important depletion of the aqueous medium, especially in its deep layers, in oxygen, a phenomenon known as eutrophication.

This algal production also increases the accumulation in the bottoms of the water bodies concerned, putrescible materials and debris of organic origin whose decomposition, by aerobic fermentation, in turn leads to overconsumption of oxygen and causes further impoverishment. from the aqueous medium to oxygen excluding any development of animal life; putrescible matter, unable to be decomposed by aerobic fermentation, then give rise to an evolution in anaerobic form with releases of gas and odors particularly unpleasant for the environment.

The invention aims to complete and develop the interest of water treatment processes and chains, especially sludge and vases from natural water reserves, current or stagnant, allowing to return to this environment significantly clean water from the point of view of suspended solids (mineral or organic), but also free of derivatives from the runoff of precipitation water on agricultural land and resulting in particular phosphatic and nitrogen compounds, sources of the disadvantages that have been described above.

To this end, the invention relates to a process for the treatment and purification of highly charged liquid media in pollutant elements in suspension and in solution, the process being of the type successively comprising a gravimetric separation phase for the removal of solid particles. of decreasing granulometry and the recovery of a clear water, and the method is characterized in that the treatment comprises, during or at the end of said solid particle separation operations, an injection phase in the liquid medium being treated. reagents suitable for precipitating, followed by removal of precipitates obtained, residues in solution from the leaching of runoff water on cropland such as phosphate and / or nitrogen compounds, allowing release into the environment natural liquid, including water deprived of nutrients with a phycogenic effect.

More particularly, in the context of the implementation of the process according to the present invention, salts are used as reagents capable of causing, by double decomposition, in the presence of the phosphate and nitrate ions to be eliminated, the formation of phosphate salts and insoluble nitrates precipitating in solid form in the liquid medium during treatment and thus may be subsequently removed by physical methods.

According to another characteristic of implementation of the process according to the present invention, the reactants are chosen from the group comprising iron salts and aluminum salts.

More particularly, the iron salts chosen as precipitation reagents for phosphate and nitrogen ions are chosen from the family comprising iron sulphate, iron chloride, double chloride salt and iron sulphate or their mixture.

The aluminum salts chosen as precipitation reagents are chosen from the family comprising aluminum sulphate and the polycondensed aluminum salts known under the trademark CUALENC.

According to another characteristic of the invention, flocculating agents such as polyelectrolytes are introduced concomitantly with the injection of precipitation reagents or after this injection.

According to a first embodiment of the process according to the invention, the precipitation reagents of the phosphate and nitrogenous ions are introduced into the medium to be treated in the form of a powder, after screening and desmaling of the sludge, resulting in an elimination of the materials in question. suspension, especially of mineral nature, corresponding to a particle size greater than about 60, the liquid medium then being in a stirred tank where it is maintained in the presence of said reagents for the time necessary to obtain the phosphate and nitrogen precipitates.

In this case, the holding time in the presence of stirring reagents within the liquid medium to be treated is prolonged for about an hour, the precipitates being removed during the subsequent dehydration phases, in particular by passing through a lamellar filter and a thickener, followed by filtration, the precipitates being collected in the filter cake.

Alternatively, inorganic compounds containing iron salts and / or aluminum salts, in particular bentonite, zeolite, illite, montmorillonite, may be introduced as powdery reagent in the medium to be treated.

The invention also relates to an alternative embodiment of the process as specified above and wherein the reagents are introduced into the liquid medium after the physical separation phases resulting in the removal of particles and suspended solids of greater particle size. at 60 A, the liquids then being circulated from the sanding station to the subsequent dewatering station, the length of the pipe being designed to allow a sufficient contact time to complete the double decomposition of the salts in the presence, before lead to the precipitation of insoluble salts, especially phosphates and nitrates of irons and / or aluminum.

More specifically in this case, flocculating agents, in particular in the form of polyelectrolytes, are introduced into the circulating medium and having already received the precipitation reagents, this introduction of the flocculating agents being at least four meters after the introduction of the precipitation reagents.

The invention finally relates to a third alternative embodiment of the specified method and characterized in that the precipitation reagents are introduced into the liquid medium after the physical purification phase and removal of solid particles and suspended solids, and after the following phase of dehydration by lamellar filter and thickener, the reactants being introduced into the liquid phase at the end of the process and the precipitate being collected by final filtration, in particular on a band filter.

In the latter case, it can also be provided that the final filtration to result in the elimination of insoluble precipitates is done on a biofilter or bacterial filter with supply of atmospheric oxygen by blowing air at the base of the filter for the purpose of ultimate degradation of the last organic particles that can remain in the water in treatment.

Other features and advantages of the invention will become apparent from the following more detailed description, which is given in connection with three embodiments of the present invention which will be successively described.

In the figures, Figure 1 gives a general diagram of the set of successive phases emphasizing in particular the physical treatment of water operations, the precipitation phase of the phosphate and nitrated ions being carried out in a stirred tank.

FIG. 2 represents an alternative embodiment of the method in which the precipitation reaction is carried out in the pipe conveying the water during treatment from the first stages of screening and grit removal to the dehydration phase.

FIG. 3 represents a third variant in which the phase of precipitation of the parasitic ions and to be eliminated is carried out on the overflow conveying the clarified water from the dehydration phases.

In a general way, the same references on the three figures will be assigned to the common organs.

In all of the figures, it is seen that the water is taken from a sludge pumping assembly, in particular by dredging, and the water is conveyed from the sludge pumping station 1 to a screen assembly 2 allowing a first elimination. debris of large particle size, the water having undergone this first separation goes to a buffer tank 3 where the recovery pump 4 brings it to a first hydrocyclone 5 or primary cyclone whose upper overflow constituting the water relatively clarified leads to the control box 10, the lower discharge of the primary hydrocyclone 5 then passes to a set of grit 6, consisting in particular of a vibrating screen possibly under vacuum, allowing a high spin and as described in the application of French patent previously cited in the name of the Applicant (No. 94.01.853).

A buffer tank 7 receives the water resulting from this first grit removal and it is recycled from the pump 8 to a secondary hydrocyclone 9, the overflow of which consists of relatively clarified water, also leads to the regulation box 10.

This water being treated is taken up in the homogenization tank 11 from which a pump 12 conveys it to the lamellar clarifier 15 overlying a thickener 14, the purified upper phase coming out of the lamellar clarifier at 15a; while the thick sludge exiting the thickener 14, conveyed from the sludge pump 16, is directed to a band filter 17, the cake being discharged for discharge or recovery, while the filtrate can be conveyed with the overflow phase of the lamellar clarifier to the original medium.

As has been explained above, the specific object of the invention is to make it possible to complete the physical operations which have just been described and which constitute a complete cycle within a processing chain, to lead to the elimination of the elements and chemical compounds in solution, thus complexing the elimination of suspended matter in the entire chain.

In a more particular way, it is sought to eliminate the compounds from the enrichment of agricultural land either by mineral fertilizers essentially phosphates or nitrates, or by amendments or fertilizers of organic origin and also having a strong load in nitrogen derivatives especially in ammoniacal form.

The strongly negative effect on the aqueous medium within the natural environment of such components has been exposed, causing the development of plant flora, especially algal flora, in stagnant or current water reserves; this accumulation of algal bodies provoking by the deposition of putrescible organic matter in the bottom of the aquatic mass a strongly negative phenomenon of eutrophication with, consequently, the death and the inhibition of the development of the natural fauna.

The production of algae can be analyzed chemically from nitrogen and inorganic phosphorus according to the following very general formula

<tb> 106 <SEP> CO2 <SEP> + <SEP> 16 <SEP> NO3 <SEP> 122 <SEP> H20 <SEP> + <SEP> 18 <SEP> H6 <SEP> + <SEP> HPO4
<tb><SEP> s <SEP><<SEP> light
###
<Tb>
The analysis and examination of this balance and the balance of compounds involved in the creation of the plant body by photosynthesis show that, for the production of 15.8g of organic plant material (algae), are consumed -lg of phosphorus in the form of phosphate ion (PO4) - and 7.2g of nitrogen (in the form of nitrate ion: NO3-).

It can thus be noted that the phyogenic action of phosphorus is much greater than that of nitrogen whose consumption is higher; we can thus deduce that it is thus much more effective to act on the medium by deficiency in phosphorus rather than in nitrogen; since to inhibit the same amount of algal body production, it is necessary to block the presence of a larger amount of nitrogen derivatives than phosphorus derivatives.

The elimination of phosphate compounds, but also nitrogen compounds (in the form of nitrate ions or ammoniacal ions) can be done at several stages of the evolution of the continuation of the treatment.

 As previously indicated, salts are used, in particular irons and aluminum, which will result in the formation of very poorly soluble metal phosphates and which can subsequently be recovered and removed with the suspended matter.

Supply of precipitation reagents in a static tank.

According to a first embodiment, the precipitation reagents are introduced into the liquid medium at the end of the screening and grit removal phase.

As previously explained, the liquid medium present in the control box 10 2 was largely separated at the screening station 2 as the primary and secondary hydrocyclones 5 and 9 and the sieve 6 particles and suspended materials of particle size up to 'to a dimension less than 60 to 50
The liquid medium being treated is then introduced into a homogenization tank 11 into which are poured, from the reservoir 11a, the powdery reagents intended to cause the precipitation of the polluting ions.

The stirrers llb and llc maintain homogeneous conditions, the medium and allow a bringing together reagents throughout the treated medium.

After a time sufficient to allow the formation reaction precipitates, the whole is taken from the pump 12 and routed to the subsequent stages of dehydration.

In this case, provision may also be made for placing in the precipitation tank flocculation agents.

The residence time and bringing the reagents into contact with the medium being treated will be at least one hour to allow the rection of the dephosphatation.

The dosage of the powdered reagent will be determined beforehand in a reduced volume test, in particular in a field laboratory test.

The use of reagents in powder form eliminates the problems of transporting and storing reagents in liquid form.

The aforementioned phosphate salts are removed in the subsequent stages of dehydration.

The reagents used in this embodiment are, as previously indicated, essentially ferric sulfate Fe SO 4 and aluminum sulfate A 12 (SO 4).

But we can use rocks or minerals containing the active ingredients above, including bentonite, zeolite, illite, montmorillonite, lime, as well as organic derivatives (coal) or biological (bacteria ).

Supply of reagents in a circulating pipe.

In this variant, illustrated in FIG. 2, the reagent is introduced after the sludge pump 12 and the pipe 12a which conveys the liquid towards the dehydration phase, that is to say towards the lamellar decanter 15, will be extended by in order to allow a stay time of the circulating water with the reagents introduced from the reserve 13.

It is advantageously possible to inject flocculating agents, in particular polyelectrolytes, preferably at a level into the pipe situated four meters after the precipitation reagents have been placed in the medium.

The stirring and the flocculation reaction will take place in the sludge pipe and the polyelectrolyte flocculates the organic materials, suspensions and microflocs, in particular precipitated phosphate.

In this form of implementation, it is advantageous to use mercury-iron chloride at a concentration of between 500 and 600 g per liter, or else a poly-condensed aluminate salt, known under the trade name ACUALENC, or even double salt. chloride and iron sulphate (Fe Cl (su4))
This mode of introduction is particularly advantageous, which does not imply any modification in the installation and, moreover, the precipitation of the iron salts in the sludge will allow the recovery of the precipitate in the final phases, in particular at the level of the thickener and, finally, the band filter 17.

Precipitation treatment in the final phase of clarified water.

Finally, it is possible to treat the clarified water issuing from one part of the lamellar clarifier and, on the other hand, from the filter press.

The advantage of this concentrated treatment on the final phase of recovery of clarified water is to finally target the only product to be treated.

It can be seen that the treated sedimented sludge has an organic content that can be high; the presence of these suspended materials, of organic and putrescible nature, can lead to overconsumption of the reaction, in particular of iron or alumina sulphate, to the detriment of the dephosphatation reactions; and, in this case, the introduction of reagents before lamellar settling is expensive.

In the particular case considered here, where the purified water still contains in the final phase organic microparticles resulting in a demand.
Biological Oxygen (BOD) significant, the final discharge waters containing phosphate, nitrate and ammoniacal ions are treated on a biofilter, after adding a dephosphating reagent as previously discussed.

The assembly is illustrated in FIG. 3, where it can be seen that the outlet of the lamellar decanter 19 joins the outlet (18) of the band filter, to undergo in the final phase the introduction of the dephosphatation reagents consisting of iron salts or of alumina previously specified.

The pipe being provided with a sufficient length to allow a suitable contact time, the final clarified water, but then containing the precipitated phosphates and some organic matter in suspension, is introduced on the bacterial filter 20.

This biofilter consists of a downflow filter for receiving and retaining precipitated phosphate and operates in aerobic mode by blowing air from line 21 to promote biodegradation of putrescible materials (BOD5) and as far as possible, the nitrification of NH4 + ions.

According to the sediment and the composition of its interstitial water, biofilters of the following sizes will be provided for a flow rate of 100 m / h.

NH4 content + applied load applied load volume of
effluents in NH4 + kT / m3xj in NH4 + kg reactor
EXTRACT j m3
2,4 4,8
5 0.5 12 24
10 24 48
Note that nitrification is a function of temperature and that in hot weather (water> 17 C) the applied load will be 1 kg / m3 x j. For colder temperatures, nitrification will be interrupted.

In the case where the effluent has a low organic suspension content (BODs <10 mg / l) and an NH4 + content <5 mg / l, it can be considered that a simple sand filter will suffice. The pollution is so low in terms of BOD5 and NH4 + that aerated filter is not needed for the maintenance of aerobic biomass, which is responsible for the removal of some of the BOD5 and nitrification of the NH4 + ion

Claims (13)

 REVENDI CMK IONS 1) Process for the treatment and purification of highly charged liquid media with pollutant elements in suspension and in solution, the process being of the type comprising successively a plurality of gravimetric separation phases for the removal of solid particle size particles decreasing and the recovery of a clear water, and the method is characterized in that the treatment comprises, during or at the end of said solid particle separation operations, an injection phase in the liquid medium during treatment of reagents capable of causing precipitation, followed by elimination of the precipitates obtained, residues in solution resulting from the leaching of runoff water on cultivated land such as phosphatic and / or nitrogenous compounds, allowing the discharge into the natural environment of a liquid, especially a water devoid of nutrients with a phycogenic effect. 2) Process according to claim 1 and characterized in that salts are used as reagents capable of causing, by double decomposition, in the presence of phosphate ions and nitrates to be eliminated, the formation of insoluble phosphate and nitrate salts precipitating in solid form in the liquid medium being treated and thus may be subsequently removed by physical methods. 3) Process according to claim 2, characterized in that the reagents are selected from the group comprising iron salts and salts ofalu -., Inium. 4) Process according to claim 3, characterized in that the iron salts chosen as precipitation reagents for phosphated and nitrogenous ions are chosen from the family comprising iron sulfate, iron chloride, double salt and sulfate sulfate. iron or their mixtures. 5) Process according to claim 3, characterized in that the aluminum salts chosen as precipitation reagents are selected from the family comprising aluminum sulfate, the polycondensated aluminate salts known under the trademark ACUALENO. 6) Method according to one of claims 1 to 5, characterized in that introduced simultaneously with the injection of precipitation reagents, or after this injection, flocculating agents such as polyelectrolytes. 7) Form of implementation of the process according to one of claims 1 to 6, characterized in that the precipitation reagents of phosphate ions and nitrogen are introduced into the medium to be treated in powder form, after screening and grit removal sludge , resulting in an elimination of suspended solids, in particular of a mineral nature, corresponding to a particle size greater than approximately 60 μ, the liquid medium then being in a stirred tank where it is held in the presence of said reagents for the time necessary for the obtaining phosphated and nitrogenous precipitates. 8) Process according to claim 7, characterized in that the holding time in the presence of stirring reagents within the liquid medium to be treated is extended over about an hour, the precipitates being removed during the subsequent dehydration phases, in particular by passage on a lamellar filter and a thickener, followed by filtration, the precipitates being collected in the filter cake. 9) Method according to one of claims 7 or 8, characterized in that introduced as a powder reagent in the medium to be treated inorganic compounds containing iron salts and / or aluminum salts, including the bentonite, zeolite, illite, montmorillonite. 10) variant implementation of the method according to one of claims 1 to 6 above and characterized in that the reagents are introduced into the liquid medium after the physical separation phases resulting in the removal of particles and materials in suspension of particle size greater than 60>, the liquids then being circulated from the sanding station to the subsequent dewatering station, the length of the pipe being designed to allow a sufficient contact time for pari the realization of double decomposition of salts in the presence, leading to the precipitation of insoluble salts, including phosphates and nitrates irons and / or aluminum. 11) Process according to claim 10, characterized in that flocculating agents, in particular in the form of polyelectrolytes, are introduced into the circulating medium and having already received the precipitation reagents, this introduction of the flocculating agents being at least four meters after the introduction of precipitation reagents. 12) variant implementation of the method according to one of claims 1 to 6 and characterized in that the precipitation reagents are introduced into the liquid medium after the physical purification phase and removal of solid particles and materials in suspension, and after the following phase of dehydration by lamellar filter and thickener, the reactants being introduced into the liquid phase at the end of the process and the precipitate being collected by final filtration, in particular on a band filter. 13) Process according to claim 12, characterized the final filtration to result in the elimination of insoluble precipitates is done on a biofilter or bacterial filter with atmospheric oxygen supply by air insufflation at the base of the filter for the purpose of degradation the last organic particles that can remain in the water at the end of treatment.